1. Field of the Invention
The present invention relates to a film bulk acoustic resonator and to a filter, a communication module and a communication device using the film bulk acoustic resonator.
2. Description of the Related Art
With the rapid spread of wireless applications typified by mobile-phone units, the demand on high performance filters and duplexers is now increasing. Filters and duplexers using a film bulk acoustic resonator (FBAR) are gaining attention as filters and duplexers of the next generation, replacing with surface acoustic wave filters, because they bring about low-loss and high withstand electric power characteristics specifically in high frequencies. A main reason why the film bulk acoustic resonator filter essentially has the low-loss and high withstand power characteristics is because the resonator has a simple structure and can avoid drop of the characteristics due to an increase of electric resistance because it can assure an electrode size even if frequency is increased. However, performances of the surface acoustic wave filter are being remarkably improved lately. Therefore it has become essential to improve the performances of the filter using the film bulk acoustic resonator further and to lower the low-loss characteristics in particular to build up its competitiveness. By being influenced by such background, developments for lowering the low-loss characteristics of the film bulk acoustic resonator further are now actively promoted.